The present invention relates to a data communication system in a mobile radio using a TDMA (Time Division Multiple Access) method or CDMA (Code Division Multiple Access) method.
FIG. 1 shows the block diagram of a conventional data communication system using the TDMA method. On a transmitting side of FIG. 1, a speech or data signal is inputted to a transmission data converter circuit 5 and supplied therein with a control signal and the like to form a frame. A resultant signal is modulated in a modulator circuit 6, converted in a transmitter circuit 7 to have a desired carrier frequency, and transmitted from a transmitting antenna 8 to a base station. On a receiving side, a receiving antenna 1 receives a signal from the base station. A receiver circuit 2 converts the received signal to a base band signal. A demodulator circuit 3 demodulates a base band data. A received data converter circuit 4 splits the base band data into a received control signal and a received speech or data signal, and outputs the received speech or data signal. A timing controller circuit 9 exercises control over every timing and sequence of the data communicattion system.
FIG. 2 shows the block diagram of a conventional data communication system using the CDMA method. On a transmitting side of FIG. 2, a speech or data signal is inputted to a transmission data converter circuit 16 and supplied therein with a control signal and the like to form a frame. A resultant signal is modulated in a modulator circuit 17, spreaded in a spreading circuit 18, then converted in a transmitter circuit 19 to have a desired carrier frequency, and transmitted from a transmitting antenna 20. On a receiving side, a receiving antenna 11 receives a signal from a base station. A despreading circuit 13 performs correlation detection. Furthermore, a demodulator circuit 14 demodulates a base band data. A received data converter circuit 15 splits the base band data into a received control signal and a received speech or data signal and outputs the received speech or data signal. A timing controller circuit 21 exercises control over every timing and sequence of the data communicattion system.
In the TDMA method, however, information which can be transmitted on one channel is determined by unit slot. In case data transmission (of high-speed data, image or the like) exceeding a transmission rate determined by unit slot is to be performed, transmission is performed by using a plurality of channels simultaneously. If the number of usable channels is insufficient when it is desired to use a plurality of channels, data cannot be transmitted, and call block is caused. The TDMA method has such a problem. In the case of the CDMA method as well, data cannot be transmitted, and call block is caused in the same way when the number of usable channels is insufficient. Furthermore, if the number of usable channels is insufficient at the time of hand over, hand over in the data communication system fails.